Conventionally, in the field of production of printed wiring boards, photosensitive resin compositions and photosensitive elements (laminated products) having a structure in which a layer formed using the photosensitive resin composition (hereinafter, referred to as “photosensitive resin layer”), is laminated on a support, and a protective layer is disposed on the photosensitive resin layer are widely used as resist materials to be used for etching, plating, or the like.
A printed wiring board is produced using such a photosensitive element, for example, by the following procedure. That is, the photosensitive resin layer of the photosensitive element is first laminated on a circuit-forming board such as a copper-clad laminate. At this time, the lamination is performed so that a surface of the photosensitive resin layer (hereinafter, referred to as “upper surface” of the photosensitive resin layer) opposite to a surface thereof (hereinafter, referred to as “lower surface” of the photosensitive resin layer) that is in contact with the support is in close contact with a surface of the circuit-forming board that forms a circuit. Therefore, in the case where a protective layer is disposed on the upper surface of the photosensitive resin layer, the laminating operation is performed while the protective layer is being peeled off. Further, the lamination is performed by thermocompression bonding of the photosensitive resin layer to the circuit-forming board that is a base (lamination under atmospheric pressure).
Next, the photosensitive resin layer is subjected to pattern exposure through a mask film, or the like. At this time, the support is stripped away at a timing, either before exposure or after exposure. Thereafter, the unexposed portions of the photosensitive resin layer are removed by dissolution or dispersion in a developer. Next, a pattern is formed by etching or plating, and the cured portions of the photosensitive resin layer are finally stripped away to be removed.
Meanwhile, as a technique for the aforementioned pattern exposure, a projection exposure method in which the photosensitive resin layer is exposed to light by irradiation via a lens with active light projecting a photomask image has been used in recent years. As a light source to be used in the projection exposure method, an ultrahigh pressure mercury lamp is used. Generally, exposure machines using the i-line monochromatic light (365 nm) as an exposure wavelength are mostly used, but the exposure wavelengths of the h-line monochromatic light (405 nm) and ihg mixed lines may be used in some cases.
The projection exposure method is an exposure method that can ensure high resolution and high alignment as compared to a contact exposure method. Therefore, much attention has been given to the projection exposure method in recent years in which circuit formation in printed wiring boards is required to be refined.
On the other hand, since the projection exposure method generally uses monochromatic light in order to obtain high resolution, the amount of irradiation energy tends to be low, and the exposure time tends to be long, as compared with ihg exposure machines or contact exposure machines. Further, whereas the contact exposure method employs one-shot exposure, the projection exposure method employs fractionated exposure, and therefore the total exposure time thereof tends to be further longer. Accordingly, the illuminance is designed to be higher in projection exposure machines than in contact exposure machines, and one exposure time in the projection exposure machines tends to be shorter than in the contact exposure machines.
With development of such a projection exposure method, a photosensitive resin composition capable of forming a resist pattern having fine line adhesion even with a short exposure time has been studied (for example, see Patent Literature 1).